Abstract

How animals use sensory information to weigh the risks vs. benefits of behavioral decisions remains poorly understood.
Inter-male aggression is triggered when animals perceive both the presence of an appetitive resource, such as food or
females, and of competing conspecific males. How such signals are detected and integrated to control the decision to fight
is not clear. For instance, it is unclear whether food increases aggression directly, or as a secondary consequence of
increased social interactions caused by attraction to food. Here we use the vinegar fly, Drosophila melanogaster, to
investigate the manner by which food influences aggression. We show that food promotes aggression in flies, and that it
does so independently of any effect on frequency of contact between males, increase in locomotor activity or general
enhancement of social interactions. Importantly, the level of aggression depends on the absolute amount of food, rather
than on its surface area or concentration. When food resources exceed a certain level, aggression is diminished, suggestive
of reduced competition. Finally, we show that detection of sugar via Gr5a+ gustatory receptor neurons (GRNs) is necessary
for food-promoted aggression. These data demonstrate that food exerts a specific effect to promote aggression in male
flies, and that this effect is mediated, at least in part, by sweet-sensing GRNs.